Lead computing gun sight



mam

Filed April 18; 1944 3 Sheets-Sheet 1 FIG.5.

Dec. 13, 1960 B. E. LUBOSHEZ 2,953,788

LEAD COMPUTING GUN SIGHT I Filed April 18, 1944 3 Sheets-Sheet 2 BENJAMIN E. L UBOSHEZ INVENTOR ATTORNEYS Dec. 13, 1960 B. E. LUBOSHEZ 2,963,783

LEAD COMPUTING GUN SIGHT Filed April 18, 1944 3 Sheets-Sheet 5 BENJAMIN E. L UBOSHE Z 1 INVENTOR BY mm United States Pateltit LEAD COMPUTING GUN SIGHT Benjamin E. Luboshez, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Apr. 18, 1944, Ser. No. 531,581

19 Claims. (Cl. 33-49) The present invention relates to lead computing gun sights, and particularly to a gyroscopically controlled sight and the gyroscopic units used.

This application is a continuation-in-part of my aban' doned application Serial No. 508,223 filed October 29, 1943.

When firing at moving targets from moving platforms, complex problems arise, both in predicting the position of the target in regard to the gun when the projectile is expected to strike, and in computing the ballistic data and applying the corrections necessary.

In the case of fixed targets being fired upon from fixed gun positions most of the problems have been satisfactorily solved, at least from a practical point of view, and the same may be said in regard to slowly moving targets constrained to move in one plane. In such cases, there is sufiicient time to ascertain the distances and other factors involved and to compute the ballistic conditions. Usually, time and effort are saved by the use of automatic predicting and computing devices, and these have proved satisfactory in practice in all cases where the movements involved are not too great.

Under aircraft combat conditions, however, both gun and target change in position and orientation so rapidly that any predicting computing device must perform its functions with great rapidity if it is to be of any use at all. So far as I am aware, the best of existing instruments require several seconds to reach correct adjustment and during that time the gunner must keep on a steady straight course and withhold his fire. Under combat conditions it is not easy to do this since the enemy is also trying to score a hit and the few seconds steady flight greatly facilitates his problem. The tendency is, therefore, for the gunner to fire before his predictor-sight is ready, or to ignore it altogether and rely upon his own unaided judgment in estimating the correct orientation of the gun. In this connection, it has been shown repeatedly in practice that even the most experienced gunners cannot possibly estimate this with sufiicient accuracy to avoid failure owing to the complex movements taking place, so that in spite of the hazard involved in waiting for the predictor-sight to reach adjustment, it is even more dangerous not to Wait for it. Any reduction in the time taken by the predicting-computing sight to reach firing adjustment is, therefore, highly desirable.

Gyroscopes have been used in connection with predicting-computing gunsights to measure the angular velocity of the target. However, so far as I am aware, gyroscopes have been used singly and for this reason considerable inaccuracies are introduced in the movement of the sight for the reason that single gyroscopes are not capable of being rendered insensitive to rotations of their supporting frame about all axes other than a given axis. In addition, single gyroscopes are disturbed by accelerational forces to which they should be neutral. Accordingly, present gyroscope controls on predictingcomputing gun sights used on airplanes are not too accurate because they are subjected to violent rotations about all three axes and are subjected to very large accelerational forces. The same is true of gyroscopically controlled predicting gun sights used on ships, tanks, trucks, etc., to a lesser degree.

One object of the present invention is to provide a gyroscopically controlled automatic predicting gun sight that shall reach firing trim in a little under a second, or at least more quickly than the gunner is ready to use it.

Another object is to provide a gun sight of the type set forth in which the movement of the sight is responsive only to rotations of the tracking member about the axis of elevation and the axis of traverse and is unaffected by rotation of the gun about any other axis due to movement of its support (airplanes, ship, etc.) in pitching rolling, etc.

And a further object is to provide a gun sight of the type set forth in which the movement of the sight is not disturbed by accelerational forces of the support on which it or its control is mounted.

And yet another object is to provide a predicting gun sight of the type set forth which automatically and continuously corrects for the range of the target and for the average velocity of the projectile.

And another object is to provide a gun sight in which the movement of the sight in each of its two directions is controlled by a gyro unit comprising two gyroscopes rotated in opposite directions with equal angular momentum and coupled together to be free to precess only in opposite directions by equal amounts.

And still another object is to provide a gyro unit control of the type set forth which can have its period of oscillation lengthened to render it insensible to small rapid accelerations of the target tracking member without rendering the same capable of being disturbed by outside accelerational forces of the unit or the support carrying the same.

Another object is to provide a predicting gun sight of the type set forth which is unaffected by rotations of the sight about the sight and/or gun axis or an axis parallel thereto.

And yet another object is to provide a gun sight of the type set forth with a gyro unit control for preventing rotations of the sight about the gun axis or an axis parallel thereto, or a gyro unit control for detecting any rotation of the gun sight about a third, or 22 axis and instigating the appropriate corrections to the sight.

The novel feaures that I consider characteristic of my invention are set forth with particularly in the appended claims. The invention itself, however, both as to its organization and its methods of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings in which,

Figures 1, 2, and 3 are diagrams showing the problems involved in computing the lead of a gun which the present invention is adapted to solve automatically, and which diagrams facilitate an understanding of the present invention.

Figure 4 is a schematic view of the combination of elements comprising a predicting-sight constructed in accordance with one embodiment of the present invention; the parts being arranged so as to facilitate showing their cooperation in one view rather than being arranged in the most satisfadory manner for practical operation.

Figure 5 is a vector diagram of a part of the linkage used in the computing mechanism of the sight for multiplying the value x prescribed by the gyro unit in accordance with the angular velocity of the target by the value of the range R alone or by the factor R/V, where V is the average velocity of the projectile.

- Figure 6 is a perspective view of an airplane carrying aaeanaa fixed machine guns and a fixed cannon and equipped with a predicting gun sight constructed in accordance with the present invention. The sight is purposely made out of scale with relation to the plane and its parts in order to clearly illustrate its form and mounting.

Figure 7 is a perspective view of the outside of the box housing adapted to house mechanism shown in Figure 4 making up the sight, and broken away to show the gyro unit for preventing rotation of the sight as a whole about the gun or sight axis, or a ZZ' axis parallel thereto.

Like reference characters refer to corresponding parts throughout the drawings.

According to the present invention the desired result is achieved with the aid of a multiple gyroscope device for detecting, and instantly applying, to any sighting device, that part of the total required angle of elevation, and/r traverse, which depends upon the angular velocity of the target as seen from the gun. Although in the present instance, a purely mechanical way of linking the gyroscopic part of the instrument with the numerous other factors involved, is described by way of example, it is pointed out that electrical and optical means for achieving the same result are within the scope of the present invention.

The basis of the method used in the present invention consists in following or tracking the target with a telescopic sight, or other sighting device, attached to, or associated with, the gun to move therewith. As the range of the target changes, the ranging part of the instrument is adjusted and at the same time the orientation of the gun is altered continuously so as to keep the target aligned in the sight. With existing instruments (such as are used on some'aircraft) if this procedure be followed for about five seconds before firing, the sight is automatically adjusted so that the gun points in the correct direction for the projectile to hit the target by the time it reaches the anticipated position.

Before considering the specific arrangement of the present invention which provides for more effective automatic sight adjustment, it might be well to point out some of the factors involved in dealing with moving targets.

Suppose in Figure 1, A represents the point of departure of the projectile, and B the position of a moving target at the instant the projectile leaves the gun. If both A and B are in motion, A can be considered fixed and B given a velocity compounded (in the usual way) from the velocities of A and B. Thus B is the position of the target relative to A. Let the distance AB, as measured by a range-finding instrument just before firing, be R. After a short time interval the target will have moved to a new position C relative to A.

Let the relative velocity of the target by v and the direction of its line of movement, with regard to the line of sight AB be Let C be the position occupied by the target after the time interval trequired by the projectile to traverse the intervening distance and strike it. The broken line AC represents the projection of the path of the projectile on to the plane which contains A, B, and C. Let the movement of the projectile be further projected upon the straight line AC and its mean velocity along this line be represented by V. Since both the target and the projectile meet after the time interval t:

Let FA be a tangent at A to the trajectory of the projectile as projected on plane ACB. The angle CAF or p depends upon various ballistic conditions, windage, etc., but not directly upon the relative velocity between the gun and target. However, corrections to this angle may be called for in so far as the changed direction and the altered range may indirectly affect the question. The effect is quite small, but it will be considered at a later stage in connection with the general problem. At the moment, attention will be focussed upon the angle CAB or 0 which is due entirely to the relative motion between the target and the gun. This is the angle of le d and is .4 the additional angle by which the gun must be turned in the direction of the apparent movement of the target in order that the projectile may strike the target.

In the triangle ABC and its exterior angle:

CB/Sin 0==AC/Sin Hence vJ/Sin 0=V.t/Sin Or Sin 8=v Sin qb/ V Suppose that the target be tracked by the gunner, i.e. kept in alignment in a sight attached to move with the gun, but with the requisite fixed angular difference between them appropriate to the firing conditions. While swinging the gun to keep the target in the sight, the gun moves with an angular velocity w which at the instant of firing is determined by the equation:

since v.Sin is the component of the targets velocity at right angles to the line of sight and R is the range of the target. Of course, w varies slightly as the target advanced along the line BC, but since the angle 0 is always reasonably small, the initial value of w is a good approximation to the average. It would be quite possible to bring in a correction to w depending upon its rate of change, but it is very doubtful whether the extra complication would be worth while.

Substituting for Sin 4: in the equation for 0:

In this equation R is the range at the instant of firing as determined by a range finder associated with the sight, and V is the average velocity of the projectile along an imaginary trajectory, which is its real trajectory projected upon the line AC. Evidently, the value of V must depend upon the distance AC as well as upon the ballistic conditions. For any given gun using a specific type of projectile, the ballistic coefficient and other ballistic factors are constant so that (if provision be made for the windage effects and other corrections depending upon gun orientation to be linked with the position in which the gun is actually pointed at the instant of fire) the projected average projectile velocity can be considered as a simple function of CA (Figure l). The magnitude of CA, or the future range, can be predicted be means of a rate-of-change-of-range device and then V can be determined with a good degree of accuracy. Since the future range is an important quantity which enters into nearly all of the ballistic calculations and corrections as well as into the time setting of the shell fuse, it is well worth while to obtain it with as great a degree of accuracy as possible. In many cases this is absolutely essential, but under the conditions of aerial combat the present range R, i.e. that measured at the instant of firing, may be used in the computations since the time intervals involved are always small.

Returning to the basic equation for the angle of lead:

it will be seen that the only factor that remains to be determined is w, the angular velocity of the target as seen from the gun.

The present invention principally concerns improvements in the means adopted for detecting this angular velocity w of the target relatively to the gun and in the means for applying the effects of these angular changes to the computation of the ballistic problem, so that an automatic correction may be applied almost instantaneously to the alignment of the gun sights.

In order to simplify the explanation, the very simplest type of gun sight will be considered, but it will readily be understood that the same principles may be applied to collimating or telescopic gun sights by imparting the requisite corrections to the graticule or optical parts in the more complicated constructions. Accordingly, it will be assumed that the gun sight consists of a fixed fore sight and an adjustable rear sight both attached to part of the gun support so as to move in elevation and azimuth with the gun in definite relationship with its bore.

It is convenient to consider the location of the target at any instant in regard to three axes mutually at right angles associated with the gun platform so as to move with it. It does not matter particularly which three axes are chosen, but for many purposes the axes chosen are: a vertical axis, a horizontal North-South axis, and a third axis at right angles to the other two. In connection with airplane guns and the present problem, it is convenient for the primary discussion to choose one axis (OZ) parallel to the longitudinal axis of the gun (and, therefore, parallel with the initial direction of departure of the projectile) a second axis (OX) at right angles to the first and in a horizontal plane when the airplane is in horizontal flight, and a third axis (OY) perpendicular to the other two, and, therefore, in a vertical plane when the airplane is in horizontal flight. All the movements can then be referred to these three axes.

For targets very close to the gun, the line of sight and the gun bore are parallel with each other, whilst for distant targets the gun must be pointed upward in relation to the line of sight. If the target is to be seen in alignment in the sight at all practical distances the rear sight must, therefore, be raised so that the line of sight makes an angle with the tangent to the trajectory at the point of departure. This is the angle of elevation (or more correctly the angle of super-elevation since target and gun may not be at the same level) and in the case of stationary targets its magnitude depends upon the five principle factors previously considered.

In the case of moving targets this angle must be increased or decreased, by an amount depending upon the range and upon that part of the angular velocity of the target (as seen from the gun) which lies in a vertical plane containing the longitudinal axis of the gun. This, the amount of increase or decrease in the normal angle of elevation, which is due to the relative motion of the target and the gun in a vertical direction may be called the angle of lead in a vertical plane.

In the same way the rear sight must be moved to the side in order that the gun may point in correct azimuth. As previously explained, the azimuth of the gun is slightly different from the true azimuth of the target because of the factors then considered, but if in addition there be relative motion between gun and target this angular dilference must be increased or decreased by an amount dependent upon the range and the horizontal component of the angular velocity of the target as seen from the gun. This is the angle of lead in a horizontal plane. If the target is being followed by the sights during its movement, the position of the rear sight must be changed laterally so that the requisite angle shall exist between the line of sight and the line of fire.

In the case of both the vertical and the horizontal projections of the total angle of lead, the angle is always in the same direction as the movement of the target, i.e., the gun is fired ahead of the present position of the target. Of course, this does not mean, for example, that the quadrant angle of elevation in the case of objects moving in a vertical sense is always greater than for stationary objects: the angle of lead is applied algebraically so that with rising targets the total angle is greater and with falling targets it is smaller.

Thus in Figure 2, suppose OZ to be an axis through the bore of the gun, OX a horizontal axis (when the vehicle carrying the gun is horizontal), and let OY be an axis perpendicular to the other two. When both the target and the gun platform are stationary, the line of sight must be moved from alignment with the gun barrel (i.e., from line g) to a new position ag which, when pointed directly at the target h, sets the gun at the correct angle so that the projectile following the trajectory gkh hits the target. If 3 represents the from sight and a the rear sight, the setting of the rear sight is ad along the OX axis and 00 along the OY axis.

Suppose now that the target be moving in the direction shown by the arrow. The rear sight must be moved to some new position b, so that when the line of sight bg is pointing at the target, the gun shall point ahead of it by the correct amount for scoring a hit. The displacement of the rear sight required to compensate for the relative movement of the gun and target is ab and the two components are df along the OX axis and ce along the OY axis. The angles of lead (using this term for that part of the total angles which is due to the target motion alone) are, therefore:

In the OX, OZ plane-dgf and in the OY, OZ planeegc. Call these angles 6,, and 0,, respectively.

The practical problem of moving the rear sight from the point a to the point b involves, first, the determination of the projections 0,, and 0,. of the total angle of lead 0, and then the means for moving the sight the requisite amounts.

Consider first the determination of the two angles 0,, and 0,. By analogy with the equation for the total angle of lead:

where w represents the component of the total angular velocity (of the target relative to the gun) which takes place about the OY axis, and w represents the component angular velocity about the OX axis. It is assumed, of course, that the target is being tracked by the gunner and it is this swinging of the gun that gives rise to the angular velocities. The determination of 0,, and 0,, therefore, involves the determination of W and w as well as the evaluation of, and multiplication by, the factor R/ V.

According to this invention 0,, and 0,. are determined by a multiple gyroscopic device. This utilizes four identical gyroscopes mounted in pairs on the gun frame so as to move with the gun in azimuth and elevation. The gyroscopes comprising each pair rotate in opposite directions and preferably have their rotational axes parallel, when in a neutral position. The precessional axes in each pair are likewise arranged to be parallel and the gyroscopes of each pair are coupled together so that they are free to precess only by equal amounts in opposite directions. The two pairs of gyroscopes are so oriented with regard to each other and the gun, that one coupled pair responds to rotations about the OX axis only, and the second coupled pair responds only to rotations about the OY axis.

The value of this device lies in the fact that each pair of gyroscopes, or gyroscopic unit, is absolutely indifierent to rotations, or components of rotations, about any axis but the one to which it is specifically designed to respond, and remains so even after the precessions have started and throughout their entire duration and extent. This is a very important and unique property of the two balanced twin gyroscope design which, as far as I am aware, has never been used in this, or any other, connection except in my novel airplane turn indicator disclosed in my abandoned US. Patent application Serial Number 508,224 filed October 29, 1943. With the four gyroscope device, precessions may be utilized over their whole range of movement (0 to degrees) and by suitable spring control the gyroscopes can be made to yield indications, or displacements proportional to the angular velocities that produced the precessions.

Referring now to the drawings, Figure 4 shows in schematic form a simple type of gun sight in which the gyroscopic device is used not only to indicate the correct angles of lead, but also to actuate the sight shifting mechanism. The exact disposition of the parts and the form of the linkages shown in Figure 4 have been influenced very considerably by the attempt to show every essential part more or less in one drawing, and to illustrate the principles as simply as possible. In actual practice the whole instrument would be contained in a small box B, see Figures 6 and 7 (probably no larger than 4" x 4 x 8"), and the connections and linkages would be suitably modified to fit into the available space in said box.

In Figure 4 only those parts are shown which are concerned with the angles of lead. Since this invention is not specifically concerned either with the means for obtaining the normal angles of elevation and traverse required for stationary targets, or with the windage and other corrections, no detailed description of particular mechanisms for carrying out these adjustments is called for. These angles cannot, however, be ignored in considering the additional adjustments for the angles of lead as will be readily seen from Figure 2 in which, it will be remembered, :1 represented the position of the rear sight before considering the angle of lead, and b the position afterwards. If in setting the angles the rear sight be moved along the OX and CY axes (at right angles to each other and to the direction of fire g) it is evident that equal intercepts along the axes would not represent equal angles, but angles whose magnitudes would depend upon the distances from the zero point. If, however, all of the movements be arranged to take place along curved paths with g as a center, the various angles may, under certain curcumstances, be considered independently. A convenient compromise (since the angles of lead are always relatively small) is to have only the movements for the setting of the normal angles of elevation and traverse take place in curved paths with g as a center.

With this arrangement the rear sight with all its attendant angle-of-lead mechanism can be moved bodily from the position 0 in Figure 2 to the position a. It is as though it had been moved along the two curved paths 0 0 and o d in Figure 3 which shows the new axes of reference for setting olf the angles of lead. In Figure 3 XX is a horizontal axis (or, on moving vehicles is a fixed axis that is horizontal only when the vehicle occupies a specific position). ZZ is perpendicular to the XX axis and is chosen so as to be coincidental with the direction a g this being the line of sight before taking account of the movements of the target. YY is perpendicular to both XX and ZZ The total angle of lead 0 is the angle (a g b and this projected upon the plane containing XX and ZZ gives the angle (a g f and in the plane containing YY and ZZ gives the angle (a g e Let these angles be 9,, and 0 respectively. Since the angles are usually small, displacements along the two axes XX and YY may be considered as proportional to the angles or their sines. it will be remembered that Sin 0 was the quantity that en tered into the equations for the angles of lead.

From Figure 3:

and since the angles are small, the error in taking their tangents, i.e., a f /a g and a e /a g instead of the sines is negligible. Then, if the distance between the front and rear sights be L,

Sin 0 =a f /L (approx.)

Sin fl a e /L (approx) In cases where the angles involved are to large for the angles and their sines and tangents to be considered equal, the appropriate corrections can easily be applied either by taking the difference into account by the insertion of appropriate cams or other mechanism, or, by making the rear sight move in curved paths with g as center, and pushing it along these curved paths the straight line distance a f and a e measured perpendicularly to Z2.

8 This refinement has not been shown in Figure 4, and only rectilinear guides are provided for the sight.

Referring now to Figures 4 and 6, the adjustable rear sight is shown at 39 at the top right-hand corner of the view. This sight has fiduciary lines XX and YY mutually at right angles, and at right angles to the ZZ axis. These are the axes of reference specified in Figure 3, not those shown in Figure 2. Of course, this particular form of fiduciary mark might not be the most convenient in practice (concentric circles adjustable in diameter for range finding might be more useful), but they are shown in that way in the drawing to form a reference frame for the whole arrangement.

Thus, for the whole instrument,

XX is a horizontal axis (or, on moving vehicles a fixed axis horizontal when the vehicle is in some specific position) YY is perpendicular to XX and ZZ is perpendicular to both XX and YY and this parallel to the line of sight, before taking account of the targets relative movement.

The sight 39 is held in a frame 38 which is arranged to slide in the YY direction within an outer frame 40. The latter is slidable in the XX direction along guides 41 fixed to the box or platform carrying all of the angle-oflead mechanism. Other fixed parts in the schematic showing are parts 47, 53, 157, 69, 73, 100, 116, 121, 124, 128, all of which parts form part of the supporting platform which moves only when swinging the gun to follow moving targets. (The small movement required for setting the normal angles of elevation and traverse can be regarded as movements of the gun from the sight-line and not vice versa.)

All the rest of the mechanism shown in Figure 4 serves to move sight 39 along XX and YY directions by the precise amounts called for by the equations:

and

Sin 9 =w R/ V If the distance between the front and rear sights be L (in the assumed simple sight) then and

y=L.w .R/ V Eq. 2

Where x and y are the actual movements of sight 39 along XX and YY respectively.

The movements x and y are applied separately to the sight by means of separate gyro units (one sensitive to rotations about the YY axis and the other sensitive to rotations about the XX axis) together with associated multiplying linkages and three-dimensional cams.

Consider first the parts concerned in applying the correct shift x of the slight 39 along the XX axis. The shift x is, of course, the movement of the sight required to give the correct value of 0 corresponding to a rotation of the gun about the YY axis when tracking the target.

The gyro unit detecting rotations of the gun about the YY axis and initiating a movement of the sight along the XX axis in accordance therewith is shown at the lower left hand corner of Figure 4. This gyro unit is practically identical with the one fully described in my above cited copending application Serial No. 508,224 filed Oetober 29, 1943 so that its construction and operation will not be discussed in too great detail herein. The gyro unit comprises a fixed supporting frame 73 carrying two identical gyroscopes 79 and 82 which normally rotate with their axes and 84 parallel to the ZZ axis. They are mounted in rings or cages 81 and 83, respectively, which give them freedom to precess about an XX axis. Suitable means, not shown here but fully disclosed in my above noted copending application, are provided for rotating the gyroscopes in opposite directions so that rotations of the unit about the YY axis cause them to precess in opposite directions. For example: if the gun be swung around to the right, the frame 73 is rotated about the YY axis in a clockwise direction (as seen from the top of the figure) and this causes the gyroscope 79 to precess about an XX axis in a counter clockwise direction, as seen from the left. At the same time the gyroscope 82 precesses in a clockwise direction about an XX axis as seen from the left. Through bevel gears 75, 76, 77, and 78 the cam drum 74 is therefore rotated under the joint efforts of the two precessions. The precessions are constrained by springs s and s connected between the two rings of the gyroscopes so that the amount of the precession, and hence the rotation of cam drum 74, is some function of the angular velocity about YY which caused the precessions. It is important to note that the precessions start immediately the rotation about the YY axis starts, and stops when equlibrium has been attained between the spring control and the precessional couples. This can be arranged to take place in a fraction of a second. Each angular velocity about YY is thus associated with a definite amount of precession and hence with a definite position of the cam drum 74. On the other hand, any rotations about other axes than the YY have no efiect whatever upon the rotation of the drum.

To bring out this fact, consider first rotation of the unit about a ZZ axis. When the gyroscopes 79 and 82 are in their initial positions their axes of rotation are parallel with the ZZ axis, and, therefore, there is no effect upon them. As soon, however, as the gyroscopes have precessed out of the initial position (under the influence of any rotations of the unit about the YY axis) their axes of rotation are no longer parallel with the ZZ axis, but make equal angles on either side of it. Components of ZZ rotation then exist which are not in line with the rotational axes of the gyroscopes and these tend to make the gyroscopes precess about an XX axis. Since, however, the gyroscopes rotate about their axes at equal speeds (or equal angular momentum) in opposite directions, and make equal and opposite angles with the ZZ axis, they try to precess in the same direction about the XX axis. This they are unable to do since they are coupled for precessions in opposite directions. Consequently, both gyroscopes being dynamically identical, they exert equal and opposite forces on the cam drum 74 which, therefore, remains unaffected. By dynamically identical I mean the gyroscopes have the same angular momentum. This condition is best obtained by having the gyroscopes physically identical and rotating at the same speed, but it could also be obtained by having one gyroscope larger or smaller than the other and rotating the smaller one at a speed sufiiciently greater than that of the larger to give the same angular momentum to both.

Consider next rotations of the gyro unit about an XX axis in their effects upon gyroscopes 79 and 80. It is evident from symmetry that whatever effects there might be are independent of the orientation of the axes 80 and 84 in the YY ZZ plane. Rotations about an XX axis, tend to make the gyroscopes precess about a YY axis, and since the gyroscopes have no freedom to precess about a YY axis, due to the manner of mounting of the rings 81 and 83 in frame 73, it is clear that there can be no gyroscopic effect at all.

There remains to be considered the ordinary inertia effects of angular acceleration about an XX axis. These effects are particularly important in airplanes, tanks, and other fast moving vehicles which are subject to violent pitching and rolling movements while moving along. The two gyroscopes 79 and 83 (considered now as nonrotating bodies) tend to remain behind due to these mentioned angular accelerations of the unit just mentioned, but since this lagging tendency about the XX axis is in the same direction for both gyroscopes, and they can only rotate in opposite directions by virtue of their geared linkage, there can be no elfect upon the position of cam drum 74.

Therefore, the rotations of the cam drum 74 are uniquely determined by the magnitude of the angular velocity of the gyro unit, or frame 73, about a YY axis, and is not disturbed by rotations or accelerations of the unit about any other axis.

A groove 64 in the cam-drum engages with a pin attached at 72 to the sliding member 71 which is preferably of square cross section. A connecting rod 70 and bell crank lever 68 transmit the movement of sliding member 71'to the sliding rod 65 through the pin and slot connection 67. The pin 66 at the other end of the sliding rod 65 moves the slotted bar 55 about the pivot point 56. By suitable design of the spring control of the gyroscopic precessions, combined with proper shaping of the cam slot in the drum 64, it is easy to arrange for the movement of the point 66, along the XX direction, to be proportional to the original angular velocity about the YY axis. In other words we have: the movement of the pin 66 is proportional to w Let this movement for a given value of w be d, then:

where k is a constant.

In order, now to obtain the correct value of x to apply to the sight for the given value of w it is necessary to take into account the variable factor R/ V and to multiply d by it. The multiplication is accomplished automatically by means of a simple link mechanism, while the values of R/V are picked off from a three dimensional cam and applied automatically.

A bar 44 slidable in the member 46 is provided with pins 45 and 43. The pin 45 is slidable in the slot 54 of the link 55, and the pin 43 is slidable in the slot 42 of the sight-frame 40. The bar 44 moves in the XX direction by amounts dependent upon the movement of pin 66 and the distance of the pin 45 from the pivot at 56. Hence, the movement imparted to the frame 40 depends upon the same factors.

Figure 5 shows how this mechanism provides a multiplying device. The triangle represents the link 55 and the movement of the pin 66 to the point 66 and of the pin 45 to the point 45'. Let d be a given movement of 66, n the length of the link 55 from its pivot 56 to point 66, and m the distance of 45 from the pivot point 56. Let the movement of the point 45 along the line XX, when at a distance In from the pivot 56, be s.

Then from similar triangles:

s/rn=d/n and s=d.m/n

Now if m be made proportional to R/ V m==k R/ V where k is a constant.

Also :1 was made proportional to W and we already have:

d=k w Hence From Eq. 1 (p. 17) it will be seen that the desired x was given by:

so that the constant L (being the distance between the front and rear sights) must be taken into account and the final equation becomes:

In designing the apparatus, convenient values are chosen for L and n as well as for the values of d to be associated with a given value of W and m associated with a given value of R/ V.

The value of m, or the distance between 45 and 56, is controlled by the up and down movement of the member 46 which slides in the guides 47. The point 50 of the rod 48 which is attached to member 46, rests upon a three dimensional cam 51 and a spring 49 maintains contact at all times. The cam 51 is mounted upon a shaft 52 which is rotatable in the bearings 53 and is also slidable back and forth by mechanisms not shown in the drawing. The purpose of this cam is to provide the desired movement to the pin 45 in order that the factor R/ V may be correctly applied.

The displacements of the point 50 are, therefore, arranged to be proportional to R/V. This is achieved by rotating the cam 51 in terms of R and translating it in terms of V. The rotation of the cam is obtained very simply by gearing the rotation of the shaft 52 with any suitable form of range finding device, not shown, the range at the instant of fire being the one used, not the predicted future range. Of course, the appropriate values of V associated with a particular range could be incorporated with the range as a single factor and then be obtained by a simple cam, if the range were the only factor atfecting V. Since V is the average projectile velocity (over an assumed straight line course) that would be a sufiiciently good approximation in certain cases and a simple cam would sufiice. However, in many cases, especially when firing with mobile guns from moving aircraft, the effects of windage and the differences in level between the gun and target must be taken into account in their effects upon the projectile speed and course.

For example when firing from an airplane forward along the line of motion, the speed of the plane must be added to the speed of the projectile in estimating the wind resistance; and when firing backwards, the difference in the speeds must be taken. More complex cases arise when firing out of the line of flight, and then azimuth angles as well as angles of elevation are affected. Of course, windage effects are not the only ones that afiect the projectile speed. Frequently the variations due to differences in altitude between the target and the gun are far more serious. For instance, at equal ranges the average bullet speed would be smaller when firing at targets above the gun than when firing at targets below the gun. On aircraft all of these variations can be taken care of with a useful (but very approximate) degree of accuracy by suitably gearing movable pinions on the gun with fixed azimuth and elevational circles on the plane, or the same results can be obtained by an electrical linkage. Whatever the means employed, the corrected value of V can be applied to the factor R/ V by arranging for the longitudinal shift of the cam 51 to take place automatically by the requisite amount. Since the particular means for correcting these variations do not form part of the present invention they will not be further considered.

It has been shown how the correct shift x can be applied to the sight in the XX direction by means of a twin gyroscope unit giving a displacement proportional to w a three dimensional cam rotating in terms of R and translated in terms of V, and a multiplying linkage combining all of these factors. The means for applying the correct shift y to the sight in the YY direction are exactly similar to those considered in connection with the 2:.

Thus two identical gyroscopes 102 and 103 are supported as shown in a fixed frame 100. The axes of rotation and 107 of the gyroscopes are parallel to" the Z2 axis (in the initial position) and the gyroscopes rotate at equal speeds in opposite directions. Any rotation of the support for the gun about a XX axis causes precessions to take place, so that the rings, or cages,

104 and 106 carrying the gyroscopes rotate about a YY axis in opposite directions. Thus, with the directions of rotation of the gyroscopes indicated by the arrows, any rotation of the gyro unit about the XX axis, say in a clockwise direction (as seen from the left), causes the gyroscope assembly including parts 102, 105 and 104 to rotate in a counter clockwise direction as seen from the top of Figure 4. Under the same conditions, the right hand gyroscope assembly including parts 103, 106 and 107 would precess in a clockwise direction (as seen from the top of Figure 4). Bevel gears 108, 109, 111 and 112 transmit the rotations to the shaft which, therefore, rotates under the combined precessions of the two gyroscopes. The gyroscope precessions are constrained in a suitable manner so that the amount of the rotation of shaft 110 can be made proportional to some convenient function of the original rotation w about the XX axes which caused the precessions. The same type of spring constraining means could be used in the present instance as is used on the previously described gyro unit, but for purposes of showing different modifications of structures which are suitable, I have shown the precessional movements of the gyroscopes 102 and 103 constrained by a coiled spring 110, similar to a clock spring, said spring having one end fastened to the frame 100 and its other end fastened to the shaft 110 to oppose free rotation of shaft 110. It is important to realize that (exactly as in the previous case) the twin gyroscopic assembly, or gyro unit, responds only to rotations or components of rotations, about a single axis, which in this instance is the XX axis, and that it is absolutely indifferent to any other rotations whatever; and furthermore, that this condition remains true however far the gyroscopes may have precessed. Rotation of the shaft 110 carries with it the cam 113 which is shaped so that the movements of the roller 114 attached to the rod 115, which is slidable in the bearings 116, is proportional to the angular velocity u' about the XX axis. The spring 115' keeps the roller 114 always in contact with the cam 113 so that the vertical movements of the pin 117 are always proportional to w Thus the link 118 is rotated about its pivot point 120 and the slidable pin 131 attached to the rod is moved with it. This multiplying mechanism is exactly similar to that already described in connection with the XX movement. The rod 130 has a pin 132 at its upper end and this engages with the slot 133 in the member 134. The movement of pin 132 in the YY' direction is thus transmitted to the sight 39 via the parts 135, 136, 137 and 38. These intermediate parts are inserted in order to show how further corrections canbe applied independently of the movements of the sight and added to the norms-.1 movements for angle-of-lead.

The part 134 carries two prongs 135 oppositely threaded at their top ends, while similar rods, oppositely threaded at their lower ends, are attached to the sight frame 38. Two long spur gears 136 meshing together are hollow and threaded internally (like turn-buckles) so that upon rotating them in opposite directions they separate the parts. Accordingly, rotation of the spur gears 136 serve to raise or lower the sight independently of any displacement already imparted by pin 132. The gears 136 are operated by the spur gear 162, bevel gears 163, and the sliding shaft 153. This shaft 158 carries a spur gear 159 which is slidablc along an elongated spur gear 160 (so as not to impede the XX movement of the frame 40). As illustrated the corrections are applied by means of the small hand wheel 161, but in practice this might be coupled to some automatically correcting device. A similar correcting device can, of

13 course, be inserted in the XX movement as well, if desired.

Returning to the rod 130, it will be seen that its movements are controlled in a manner almost identical with the one described in connection with rod 44 which was concerned with the XX movement; thus the rod 130 is free to slide up and down in the sleeve 129 attached to the rod 126. The latter is fixed to a sliding member 127 which is free to move in the guides 128. The far end of rod 126 forms a rounded contact point 125 which is pressed onto the surface of a threedimensional cam 122. This is similar to (although not necessarily identical with) the corresponding three-dimensional cam 51. The tWo cams fulfill identical functions in applying the factor R/ V to the movements, and for many purposes a single cam could be used to operate both the XX and the YY movements. For example, in that case the rod 126 could be connected to the rod 48 by means of a bell crank lever, and then the cam 51 would operate both rods 44 and 130.

In other arrangements the whole mechanism might be inverted. For example, the gyroscopes could be used to move the rods 44 and 130 (at right angles to their lengths) instead of the R/V cams providing this movement, while the two slotted bars 55 and 118 would be moved by rods attached to the R/ V cams. The multiplying mechanism would, of course, work just as well with this disposition, and if the R/V factors were the same for both the XX and YY effects a single slotted bar arranged as a bell crank would serve the purpose i.e., the two slotted bars 55 and 130 would be joined at the elbow and its movements would be controlled by a single R/ V cam.

A significant difiiculty in existing auto-predicting sights is the fact that the movable sight member tends to vibrate more or less rapidly in one or both of its directions of movement due to errors in tracking. Experiments have shown that it is impossible for a person under normal operating conditions to track a target smoothly. By this I mean that unbeknown to the operator himself, instead of tracking the target smoothly at all times he unconsciously periodically accelerates ahead of the target, then stops until the target catches up, picks up the target again and goes on like this over the entire tracking period. These repeated accelerations and decelerations, although apparently minute, are picked up by the single gyroscope controls heretofore used, and unwanted proccssional movements of the gyroscopes re sult in a very annoying vibration in the rear or movable sight.

With the gyroscope control of the present invention these unavoidable errors in tracking can be ironed out by damping (or averaging out) movements of the gyroscopes controlling the gun sight. This can be readily accomplished in the present mechanism by increasing the moment of inertia of the gyroscopes about their precessional axes. This can be done in several different ways, one of which might be to make the gyroscope wheels thicker without increasing their diameter, in the form of cylinders instead of the usual disc shape, and a second way, might consist of making the gyro wheels in the form of two discs spaced at opposite ends of an axle, the precessional axes passing through the axle at a point intermediate the two discs. A third way is to load the nonrotating parts that move only when precession takes place. Making the moment of inertia about the precessional axes greater than the moment of inertia about the rotational axes is conducive to increasing the time of oscillation of the gyroscopes so that they are not affected by repeated small accelerations and decelerations but tend to average out these small accelerations and decelerations due to errors in tracking. It is to be noted that this increase in the moment of inertia about the precessional axis does not directly affect the sensitivity of response but only the time taken to reach the position of equilibrium.

This idea of damping the movement of the gyroscopes by altering the moments of inertia about the precessional and rotational axes to a relationship just the opposite of that ordinarily found in gyroscope design (in normal gyroscope designs the moment of inertia relationship in question is usually that of a disc in which the moment of inertia about the rotational axis is twice that about the precessional axis) is adaptable to the present gyro units without any diificulty, but is not adaptable to single gyroscopes normally used. Accordingly, this damping effect is obtained in the present invention by making the moment of inertia about the precessional axes at least twice as much as the moment of inertia about the rotational axes. This fact will be understandable when it is remembered that to increase the moment of inertia about the precessional axis necessitates increasing the weight of the gyroscope when it is considered as a mass. It would not be feasible to apply this correction to a single gyroscope control due to the fact that the ordinary inertia effects of angular acceleration about the XX and/or YY axes would be increased to an intolerable amount. However, with the present gyroscope control units, increasing the mass of the gyroscopes is immaterial because by the unique coupling of the gyroscopes the inertia effects of angular accelerations of the unit about the XX and/or YY axes have no effect upon the position of the cam drum 74 or the cam 113.

It has been pointed out that some of the difficulties in the design of gyroscopic angle-of-lead predicting gun sights arise through the necessity of damping the precessional movements of the gyroscopes. Apart from the damping problems themselves, there are certain secondary problems, the most serious of which arises through the fact that the damping necessarily delays the movements of the sight member which takes place in response to the two components of the angular velocities concerned when tracking the target. Thus, by the time the sight reaches its final setting, the gun has changed its orientation and consequently the sight which'is attached to the gun has changed its orientation. This is of no great importance so long as the orientation of the gun has only changed about the two axes which were the axes concerned in measurement of the two components of the angular velocity of the targets as seen from the gun (axes XX and YY in the present instance), but serious errors arise when the gun orientation changes about a third axis (the ZZ axis in the present instance).

The movement of the gun in tracking the target causes the gyroscopic units to change the line of sight from a g to h g (see Figure 3) so that (in the disclosed simple sight) the rear sight member 39 moves from a to b This movement is made up of a component a f along the XX axis and a component a e along the YY axis.

Owing to the damping previously mentioned, the movements of the rear sight member 39 take place in response to rotation that had occurred a short time previously and, assuming that the magnitudes and directions of these rotations had remained constant during the interval, the movements imparted to the sight member would remain correct so long as the sight had not been rotated about the ZZ or gun, axis since the measurements for the setting took place. In other words, the sight was correctly set along the XX and YY axes and would have remained so as long as nothing had happened to alter the directions of the XX and YY axes in space about the ZZ axis during the short time interval. There may be many causes for such rotations, especially in cases where the gun is mounted on moving vehicles, e. g. aircraft, tanks, and ships, which are subject to violent movements. For instance, in the case of fighter planes carrying fixed guns, any rolling movements of the plane will involve rotation about the ZZ axis. However, evenwhen tracking with an anti-aircraft gun mounted on a fixed platform, movements in traverse must always be accompanied by a component rotation about the ZZ axis and the magnitude of this component varies from zero when the ZZ axis is horizontal to a maximum when the ZZ axis is in the zenith position, in which case, of course, all of the rotation of traverse is a rotation about the ZZ axis. Thus in practice the sight is rotated more or less around the ZZ axis and hence the imaginary XX and YY' axes rotate with it, so that the point b (Figure 3) rotates about ZZ as tracking proceeds.

This would not matter if the position of h always corresponded to that prescribed by the rotations about the XX and YY' axes, whatever their instantaneous positions in space. As has been pointed out above, in practice this condition is not even approximately realized owing to the necessity of averaging out the tracking movement and damping the gyroscope precession to a period of one or two seconds.

The present invention includes means for detecting the rotations of the sight about the ZZ, or gun, axis and applying the appropriate corrections to the sight to overcome or otfset the errors in the final setting of the sight which would emanate from such rotations about the ZZ axis.

In Figure 7 I have shown a specific modification of such a means which is applicable to existing sights as well as to my new form of sight described above and shown in Figure 4. In Figure 6 I have shown my sight, including the modification, associated with an airplane carrying fixed guns which are aimed by maneuvering the plane. According to this modification, the gun sight unit is pivoted so that the ZZ axis passes through the center of gravity of the unit and weak centralizing springs are then used to keep the unit in normal relationship with the gun. A stabilizing device consisting of twin identical gyroscopes linked for precession in opposite directions (as described previously) is used to stabilize the sight unit about the ZZ axis.

Referring now to Figures 6 and 7, the mechanism making up the sight unit is mounted in the top of the box B, and in the present instance the mechanism would include that shown in Figure 4. The rear sight member 39 which in the present instance is adjustable along the XX and YY' axes is at the rear of the box and the front sight member 300 is in the front of the box in alignment therewith. In the bottom of the box B, or in a separate box attached to the bottom of the box containing the complete sight unit, is mounted in a twin gyro stabilizing unit 201. As shown, the complete unit (including the sighting unit and the stabilizer) is pivoted on a pair of brackets 202 which are fixed to the fuselage of the plane and in the cockpit, so that the ZZ axis passes through the center of gravity of the complete unit. Centrailzing springs 203 and 204, connected to the unit and the brackets, tend to keep the unit in normal relationship with the gun.

The stabilizing unit comprises two identical gyroscopes 205 and 206 having their rotational axes 207 and 207 parallel to each other and extending along the XX axis perpendicular to the ZZ axis. Each of the gyroscopes is pivotally mounted in the base of the box so that their axes of precession are parallel to each other and extending along the YY' axis perpendicular to the ZZ axis. This mounting may include posts 208 and 208' extending from the cases of the respective gyroscopes and being rotatably mounted in the bottom of the box by suitable thrust bearings, not shown. Accordingly, by virture of this relationship of the gyroscopes they will each tend to precess about the YY axis when the whole unit is rotated about the ZZ axis and a reaction will be set up which will resist rotation of the unit about the ZZ axis. As explained above, the two gyroscopes are positively connected together so that they are capable of processing only in opposite directions by equal amounts. As shown, this coupling may comprise a pair of bevel gears 209 and 209' fixed to the respective posts 208 and 208' of the gyros and interconnected by a shaft 210 having a 16 bevel gear 211 on each end meshing with said gears. The two gyroscopes are normally returned to their central position of precession by the action of a light tension spring 212 connected at opposite ends to eyes 213 fixed in the gyro cases.

By virtue of this arrangement of the twin gyroscopes, the stabilizer will be insensitive to any rotation of the sight unit about any axis other than the ZZ axis, and the stabilizer unit will in no Way effect the proper responsiveness of the two gyroscopic units of the sight unit which control the setting of the sight. On the other hand, any rotation of the unit about the ZZ axis, and to which the gyro units of the sight mechanism are insensitive, will cause the gyroscopes 205 and 206 to precess in opposite directions by equal amounts and to set up a reaction which will oppose such rotation and thereby stabilize the complete unit about the ZZ axis. As mentioned before, the two gyros of the stabilizing unit need not be physically identical and be driven at the same speed, but must have the same angular momentum.

With the modification disclosed, rotations of the gun about the ZZ axis, caused in this instance by rolling of the plane carrying the gun, tend to drag the sight around against the action of the stabilizing gyroscopes and the springs 203 or 204 stretch in consequence. The period of oscillation with a single gyroscope in the stabilizer would be T =21rCw /\/m n,

or with two gyroscopes as shown would be:

where C is the moment of inertia of a stabilizing gyroscope about its rotational axis, w is its angular velocity, m, is the restoring couple per unit angular displacement (in circular measure) due to the spring attachments 203, 204, to the gun or its support, and n is the restoring couple (per unit angle) of the centralizing means (spring 212) acting about the precessional axis. Appropriate damping means, not shown, would, of course, be employed in conjunction with the springs. This type of twin gyro stabilizer with damped centralizing springs is fully disclosed in my copending patent application, Serial Number 515,715, filed December 27, 1943, now Patent 2,432,430, granted December 9, 1947.

According to a slight modification of this invention the complete gunsight unit including the gyro stabilizer may be pivoted about the ZZ axis so as to be slightly pendu lous. Then by shifting the center of gravity of the instrument the period of oscillation of the complete unit is made long enough to delay the unit from rotating appreciably during the period required by the sight mechanism to reach firing adjustment. This modification ditfers from that disclosed only in that the need for the centralizing springs 203 and 204 is eliminated by pendulously mounting the unit.

Another simple way of obtaining this desired result consists in arranging for the auxiliary gyroscopic unit (above used as a stabilizing unit) to rotate the sight unit, including the angle of lead computing gyroscopes and associated mechanism, around the ZZ axis in the reverse direction to the component rotation about the ZZ axis that might be taking place. The exact amount of this reverse rotation imparted to the sight, around the ZZ axis in the reverse direction to the component rotation about the ZZ axis that might be taking place, depends upon the damping of the lead computing gyroscopes and associated mechanism and the constants of the auxiliary correcting mechanism as well as upon the magnitude of the rotation about the ZZ axis giving rise to the correction. Freedom to rotate the sight about the ZZ axis can be secured by mounting the box containing the lead computing sight upon a sector concentric with the ZZ axis. A motor and relay system can be used to move aoasnss 17 the sight through the requisite angle in response to the indications of the auxiliary gyroscopic unit.

If the lead computing sight were such as to be adjusted to firing trim by optical methods, such as the adjustment of mirrors, prisms, etc., as well known in the art, rather than having the rear sight shifted along two axes as shown, the present invention could be applied equally well to account for rotations of the sight about the ZZ axis. Furthermore, while I have shown the use of coupled gyroscopes for compensating for rotation of the sight unit about the ZZ axis it is obvious that a single gyroscope in suitable orientation and mounting could be used to detect rotations of theunit about the ZZ axis. The twin gyroscope arrangement is preferred, however, because it is sensitive only to rotations having components about a single selected axis and is insensitive to rotations or accelerations about any other orthogonal axis.

In connection with the schematic representation of the mechanism shown in Figure 4 the various mechanical refinements for prevention of slack so as to give positive movement have been omitted. Furthermore, no attempt has been made to show the parts correctly balanced. In practice, however, it is important that all of the moving parts be dynamically balanced to avoid unwanted displacements when the instrument is subjected to sudden shocks or other accelerations.

It is also pointed out that certain refinements, other than those shown, suggest themselves. Some of the ballistic factors depend upon a knowledge of the true vertical and/or horizontal so that any computations based upon a reference plane fixed in regard to an airplane must be in error by an amount depending upon the orientation of the plane. No attempt has been made in this disclosure to devise means for automatically applying the normal angles of elevation and traverse, since that part of the problem appears to have been satisfactorily solved with existing equipment.

For the purposes of disclosure, a simple type of gun sight with fixed front sight and movable rear sight has been considered. This is not the only, or necessarily the best, method of carrying out the idea in practice. A useful method for many purposes is to swivel the whole sight, about the XX and YY' axes both for the normal angles of elevation and traverse, and for the angles of lead. It is a simple matter to adapt the present mechanism to suit this or other methods that might proveconvenient with various types of guns.

As far as I am aware, most existing automatic sights utilize one or more single free gyroscopes to measure the angle of lead. Since, however, it is an inherent property of a disturbed gyroscope that it shall precess spirally to its new position of equilibrium, it is difiicult to see how such a device can be made to function without a time delay occurring while the spiraling evolution is taking place. The present gyroscope control unit, on the other hand, responds immediately to the impressed rotations and reaches a position of equilibrium very rapidly. A device using only two single, constrained gyroscopes, in suitable orientation, would possess some of the advantages of the device described in the present application, but it does not appear possible in that case to eliminate the serious errors that would arise immediately the gyroscopes have precessed from their normal orientation. This is particularly true in connection with aerial gunnery or fixed guns on fighter planes where the gun may be subjected to movement about all possible axes. Four gyroscopes, arranged as set forth, together with the two gyroscopes for stabilizing the unit about the gun axis are the minimum number capable of separating the various rotations in a practical manner.

I have pointed out how and why rotation of the gun sight about the gun axis, or an axis parallel thereto, introduces errors into the final setting of the sight which are material in some cases, particularly where the gun sight is mounted on a moving vehicle where it is subject to movement about all possible axes. So far as I am aware, no one prior to the present invention appreciated that the errors in existing predicting gun sights were due, in large part, to rotation of the sight about an axis parallel to the gun, and if anyone did appreciate the fact, they never did devise or suggest a means for eliminating such errors. Consequently, it is believed that applicant is the inventor of the broad idea of detecting and correcting for rotations of the gun sight about an axis parallel to the gun axis and/or sight axis not only in connection with the particular type of sight disclosed but in combination with any type of predicting sight which might be subject to such deleterious rotation.

While I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted to the specific details of construction shown and described, but is intended to cover all modifications coming within the scope of the appended claims. I

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. In a lead computing gun sight the combination with a fixed front sight connected with the gun to move therewith, a movable rear sight carried by the gun and movable relative to said fixed sight in accordance with the elevational and traverse movement of the target relative to the gun position, of means for moving said movable sight relative to said fixed sight in accordance withthe angular velocity of the target in space relative to the gun position, aid lapt n gnti o ned 11339;} comnn sin ...a..pair

gf glmmadhiqglg e rotate about two mutually perpendicular axes associated"w'itli"'tHe elevational and traverse movement of the target relative to the gun position, each unit including a pair of gyroscopes mounted for precession in only one plane about precessional axes which are parallel, means for rotating said two gyroscopes at the same angular momentum in opposite direc tions, means for coupling said gyroscopes whereby they are limited to precession by equal and opposite amounts, means for constraining the precession of said gyroscopes so that the amount of precession thereof is a function of the angular velocity of the unit about an axis at right angles to the precessional axes of the gyroscopes, means for movably mounting said units relative to the gun position so that the precessional axes of one unit are at right angles to the elevational axis of the target relative to the gun position and the precessional axes of the other unit are at right angles to the traverse axis of the target relative to the gun position said movable sight being moved in one or both of said directions in accordance with the amount and direction of the precessional movements of the gyroscopes of the respecttive gyro units and consequently in accordance with the angular velocity of the target with respect to the gun position, and gyroscopic means for stabilizing the complete gun sight about an axis parallel tothe gun axis.

2. In a lead computing gun sight the combination with a sight member movable in two directions in accordance with the elevational and traversing movement of the gun in tracking a moving target, of means for moving said sight member in one of said directions in response to an elevational movement of the gun, and means for moving said sight member in the other direction in response to a traverse movement of the gun, each of said means including a gyro unit comprising a pair of gyroscopes mounted for precession in only one plane about precessional axes which are parallel, means for rotating said two gyroscopes at the same angular momentum in opposite directions, means for coupling said gyroscopes whereby they are limited to precession by equal and opposite amounts, and means for constraining the precession of said gyroscopes so that the amount of precession thereof is a function of angular velocity of the unit about an axis at right angles to the precessional axes of the gyroscopes, means for associating said units with the gun so that the precessional axes of one unit are at right angles to the elevational axis of the gun and the precessional axes of the other unit are at right angles to the traverse axis of the gun, said sight member being moved in one or both of said given directions in accordance with the amount and direction of the precessional movements of the gyroscopes of the respective gyro units, and consequently in accordance with the angular velocity of the target with respect to the gun po sition.

3. A lead computing gun sight according to claim 2, including means for mechanically connecting the sight member to each of the gyro units so as to be moved by and in accordance with the amount and direction of the precessional movements of the gyroscopes forming a part thereof and consequently in accordance with the angular velocity of the target.

4. A lead computing gun sight according to claim 2, in which the sight member is connected to each of the gyro units to be moved by and in accordance with the amount and direction of the precessional movements of the gyroscopes forming a part thereof and consequently in accordance with the angular velocity of the target, and means for modifying the movement of said sight in accordance with the range of the target, whereby the angle of lead is based on the range of the target as well as angular velocity of the gun in tracking said target.

5. A lead computing gun sight according to claim 2, in which the sight member is connected to each of the gyro units to be moved by and in accordance with the amount and direction of the precessional movements of the gyroscopes forming a part thereof and consequently in accordance with the angular velocity of the target, and means for modifying the movement of said sight memher in accordance with the range of the target and average velocity of the projectile, whereby the angle of lead of the gun is based on range of the target and velocity of the shell as well as angular velocity of the target in tracking.

6. A lead computing gun sight according to claim 2 which includes two independent mechanisms connected to said sight member to move it in said two directions, each of said mechanisms arranged to be actuated by the precessional movements of the gyroscopes of different ones of the gyro units and consequently in accordance with the angular velocity of the target, and means for altering said mechanisms in accordance with the range of the target, whereby the movement of the sight member is based on both of the angular velocity of the gun in tracking and the range of the target.

7. A lead computing gun sight according to claim 2 in which a pair of linkages are provided for moving said sight member in said two directions, one linkage being arranged to be actuated by the precessional movements of the gyroscopes of one gyro unit, and the other by the precessional movements of the gyroscopes of the other gyro unit to cause a movement commensurate with the angular velocity of the target, and means for altering the mechanical advantage of said linkages in accordance with the range of the target, whereby the movement of the sight member relative to the gun is corrected for the range of the target.

8. A lead computing sight according to claim 2, in which a pair of linkages are provided for moving the sight member in said two directions, one linkage being arranged to be actuated by the precessional movements of the gyroscopes of one gyro unit, and the other by the precessional movements of the gyroscopes of the other gyro unit to cause a movement commensurate with the angular velocity of the target in elevational and traverse movement, and means for automatically altering the mechanical advantage of said linkages in accordance with the range of said target, whereby the ultimate movement of the sight member is corrected for range of the target.

9. A lead computing sight according to claim 2, in which a pair of linkages are provided for moving the sight member in said two directions, one linkage being arranged to be actuated by the precessional movements of the gyroscopes of one gyro unit, and the other by the precessional movements of the gyroscopes of the other gyro unit to cause a movement commensurate with the angular velocity of the target in elevational and traverse movement, and a cam controlled means for continuously, automatically altering the mechanical advantage of said linkages in accordance with the range of said target, whereby the angle of lead of the gun as defined by the position of the sight member is corrected for the range of the target.

10. In a lead computing gun sight the combination with a sight member movable in two mutually perpendicular directions in accordance with the elevational and traversing movement of the gun in following a moving target, of means for moving said sight member in one of said directions in response to an elevational movement of the gun, and means for moving said sight member in the other direction in response to a traverse movement of the gun, each of said means including a gyro unit comprising a frame adapted to move with the gun, a pair of dynamically identical gyroscopes mounted on the frame so as to be capable of precession about only one of the two normal axes of precession, means for rotating said two gyroscopes at the same angular momentum in opposite directions, and means for coupling said two gyroscopes so that they are free to process only in opposite directions by equal amounts, said gyro units mounted relative to one another so that the rotation axes of all gyroscopes are normally parallel and so that the axes of precession of one unit are perpendicular to the axes of precession of the other pair, and so that one pair precesses only in response to a traverse movement of the gun and the other pair precesses only in response to an elevational movement of the gun, and means for connecting each of said gyro units to said sight member whereby the precessional movement of the gyroscopes of one unit controls the amount of movement of said sight member in one direction and the precessional movement of the gyroscopes of the other unit controls the amount of movement of the sight member in the other direction.

11. A lead computing gun sight according to claim 1, in which the moment of inertia of the gyroscopes about their precessional axes is greater than the moment of inertia about their rotational axes, whereby the gyroscopes are given a longer period of oscillation and rendered slower in response to instantaneous changes in acceleration of the gyro units in tracking a target, with the result that the jerky movement of the sight due to such instantaneous changes in acceleration is smoothed out.

12. A lead computing gun sight according to claim I in which the gyroscopes are constructed to have a moment of inertia about their precessional axes at least twice the moment of inertia about their rotational axes, and for the purpose of increasing the period of oscillation of the gyroscope to smooth out the movement of the sight due to instantaneous changes in the acceleration of gyro units in tracking a target.

"13. In an apparatus for directing a gun on a moving target, the combination with a sighting device, means for moving said sighting device in elevation and traverse to maintain it on a moving target, and including a pair of gyroscopes connected to said sighting device so as to be responsive respectively to the speed of said elevation and traverse movements for adjusting said sighting device in elevation and traverse, of gyroscopic means for eliminating errors in the adjustment of the sighting device which would be due to rotation of the device about an axis parallel to the gun axis.

14. In an apparatus for directing a gun on a moving target, the combination with a sighting device, means for moving said sighting device in elevation and traverse to maintain it on a moving target, and including a pair of gyroscopes connected to said sighting device so as to be responsive respectively to the speed of said elevation and traverse movements for adjusting said sighting device in elevation and traverse, of gyroscopic means associated with said sighting device and so oriented as to stabilize the sighting device against rotations about an axis parallel to the gun axis.

15. An apparatus according to claim 13 in which the gyroscopic means comprises a pair of gyroscopes having equal angular momentums and positively coupled so as to be free to precess only in opposite directions by equal amounts, said two gyroscopes being so disposed that their respective rotational and precessional axes are parallel to each other and at right angles to a third axis which is parallel to the gun axis.

16. An apparatus according to claim 14 in which the entire mechanism is arranged to move as a unit which is pivoted on an axis parallel to the gun axis and the gyroscopic means comprises a pair of identical gyroscopes positively coupled so as to be free to precess only in opposite directions by equal amounts, said two gyroscopes being so disposed that their respective rotational and precessional axes are parallel to each other and at right angles to a third axis which is parallel to the gun axis.

17. An apparatus according to claim 14 in which the entire mechanism is contained in a housing to move as a unit, said housing pivoted to rotate about an axis parallel to the gun axis and passing through the center of gravity of the unit, means for constraining said housing against rotation about its pivotal axis, and the gyroscopic means comprises a pair of identical gyroscopes positively coupled so as to be free to precess only in opposite directions by equal amounts, said two gyroscopes being so disposed that their respective rotational and precessional axes are parallel to each other and at right angles to a third axis which is parallel to the gun axis.

18. A lead computing sight according to claim 10 and including a gyroscopic means for stabilizing the sight member against rotation about an axis parallel to the gun axis.

19. A lead computing sight according to claim 10 in which the entire mechanism is arranged to rotate as a unit about an axis parallel to the gun axis and including a gyroscopic stabilizer associated with said mechanism to move as a part of the unit and for stabilizing the unit against rotation about said pivotal axis.

References Cited in the file of this patent UNITED STATES PATENTS 1,372,184 Minorsky Mar. 22, 1921 1,692,412 Koenig Nov. 20, 1928 1,758,273 Becker et al May 13, 1930 1,933,493 Chessin Oct. 31, 1933 1,936,442 Willard Nov. 21, 1933 1,999,897 Fieux Apr. 30, 1935 2,356,189 Tufts Aug. 22, 1944 FOREIGN PATENTS 18,504 Great Britain Aug. 26, 1904 130,095 Great Britain July 31, 1919 

